When traveling, always pack an extra pair of underpants. For instance, if you plan to spend six days out and about, be sure to pack at least seven pairs. This way, if you happen to shit yourself at any moment during your trip, you'll have the extra pair ready to go. Just slip the "destroyed" pair off, slide them in the nearest gas station garbage can, smack yourself in the goodies with a bottle full of Lysol wipes, and slide on the fresh, clean pair. Problem solved.
(But if you happen to shit yourself two or more times that week, you're on your own. It might be best at that point to cancel the remainder of your trip and drive straight to some type of clinic.)